1. Field of the Invention
The present invention relates to an integrated gyroscope of semiconductor material.
2. Description of the Related Art
As is known, integrated gyroscopes of semiconductor material, made with MEMS (Micro-Electro-Mechanical Systems) technology, operate according to the theorem of relative accelerations, exploiting the acceleration of Coriolis. In particular, when a linear velocity is applied to a mobile mass rotating with a constant angular velocity, the mobile mass xe2x80x9cfeelsxe2x80x9d an apparent force, called Coriolis force, which determines its movement in a direction perpendicular to the linear velocity and to the axis of rotation. The apparent force can therefore be detected by supporting the mobile mass with springs which allow it to move in the direction of the apparent force. According to Hooke""s law, this movement is proportional to the apparent force and so detecting the movement of the mobile mass allows detecting the Coriolis force and therefore the angular velocity.
In gyroscopes of the considered type, the movement of the mobile mass is detected capacitively, measuring the capacitance variations caused by the movement of mobile sensing electrodes integral with the moving mass and interfaced or interleaved with fixed sensing electrodes.
Embodiments of integrated gyroscopes in MEMS technology are described, for example, in U.S. Pat. Nos. 5,604,312, 5,275,047 and WO 97/15066 assigned to Robert Bosch GmbH and in U.S. Pat. No. 5,955,668, WO 99/19734 and WO00/29855 assigned to IRVINE SENSORS CORPORATION. However, these gyroscopes have some drawbacks.
For example, U.S. Pat. No. 5,604,312 describes a gyroscope formed by an oscillating mass and an accelerometer mounted on the driving mass. This known gyroscope requires a complicated manufacturing process which uses two different structural layers, with consequent high manufacturing costs, poor reliability, complication in aligning the accelerometers and the oscillating masses and complication in the connections.
U.S. Pat. No. 5,955,668, WO 99/19734 disclose an external oscillating mass connected to an internal sensing mass, and therefore two independent mechanical parts which may be suitably calibrated. However, for the circular gyroscope (U.S. Pat. No. 5,955,668), the structure is sensitive to stress due to the manufacturing steps and to thermal drift, since the suspension springs of the sensing mass inside the external oscillating mass are very stiff in the direction of the axis of the angular velocity and it is not possible to anchor the sensing mass in the center because the gyroscope would feel the velocity of several axes at the same time and would become unusable. Vice-versa, for the rectangular gyroscope (WO patent 99/19734), the system is not optimized because it uses suspension springs which involve undesired rotational contributions; moreover the described gyroscope does not allow the rejection of linear accelerations. Moreover, in both cases, but particularly in the case of the translational gyroscope, numerous interconnections extend under the mass, and the interconnections are rather long, with the risk of capacitive couplings with the sensing structures and therefore of distortion or imprecision of reading.
An embodiment of the invention provides a gyroscope in MEMS technology which solves the problems presented by prior art gyroscopes, and in particular is not affected by undesired capacitive couplings. Conveniently, the gyroscope according to the invention must be as far as possible insensitive to process spreads, to residual stress due to manufacturing steps and to thermal drift.
According to an embodiment of the present invention, an integrated gyroscope is provided.
In practice, the gyroscope is formed by a driving system including a driving mass having an open concave shape; an accelerometer including a sensing mass and mobile sensing electrodes; a mechanical connection (linkage) which connects the driving mass to the sensing mass. The sensing mass is surrounded on three sides by the driving mass and has a peripheral portion not facing this mass. The mobile sensing electrodes are integral with the sensing mass from the peripheral portion not facing the driving mass and are interleaved with fixed sensing electrodes. In this way, no electrical connections extend below the sensing mass. According to another aspect of the invention, the linkage includes springs placed equidistant from the center of gravity of the accelerometer, and according to yet another aspect, the gyroscope is anchored to the substrate through anchoring springs equidistant from the center of gravity of the assembly formed by the driving system and by the accelerometer.
A method of operation of the device is also provided, according to an embodiment of the invention.